libcamera: yaml_parser: Replace ok flag to get() with std::optional

The YamlObject::get() function takes a default value and an optional
bool ok flag to handle parsing errors. This ad-hoc mechanism complicates
error handling in callers.

A better API is possible by dropping the default value and ok flag and
returning an std::optional. Not only does it simplify the calls, it also
lets callers handle errors through the standard std::optional class
instead of the current ad-hoc mechanism.

Provide a get() wrapper around std::optional::value_or() to further
simplify callers that don't need any specific error handling.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Naushir Patuck <naush@raspberrypi.com>
Tested-by: Naushir Patuck <naush@raspberrypi.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>

include/libcamera/internal/yaml_parser.h

@@ -9,6 +9,7 @@
 
 #include <iterator>
 #include <map>
+#include <optional>
 #include <string>
 #include <vector>
 
@@ -165,7 +166,13 @@ public:
 #else
 	template<typename T>
 #endif
-	T get(const T &defaultValue, bool *ok = nullptr) const;
+	std::optional<T> get() const;
+
+	template<typename T>
+	T get(const T &defaultValue) const
+	{
+		return get<T>().value_or(defaultValue);
+	}
 
 	DictAdapter asDict() const { return DictAdapter{ dictionary_ }; }
 	ListAdapter asList() const { return ListAdapter{ list_ }; }

src/libcamera/yaml_parser.cpp

@@ -31,12 +31,6 @@ namespace {
 /* Empty static YamlObject as a safe result for invalid operations */
 static const YamlObject empty;
 
-void setOk(bool *ok, bool result)
-{
-	if (ok)
-		*ok = result;
-}
-
 } /* namespace */
 
 /**
@@ -100,54 +94,52 @@ std::size_t YamlObject::size() const
 }
 
 /**
- * \fn template<typename T> YamlObject::get<T>(
+ * \fn template<typename T> YamlObject::get<T>() const
- *	const T &defaultValue, bool *ok) const
  * \brief Parse the YamlObject as a \a T value
- * \param[in] defaultValue The default value when failing to parse
- * \param[out] ok The result of whether the parse succeeded
  *
  * This function parses the value of the YamlObject as a \a T object, and
  * returns the value. If parsing fails (usually because the YamlObject doesn't
- * store a \a T value), the \a defaultValue is returned, and \a ok is set to
+ * store a \a T value), std::nullopt is returned.
- * false. Otherwise, the YamlObject value is returned, and \a ok is set to true.
  *
- * The \a ok pointer is optional and can be a nullptr if the caller doesn't
+ * \return The YamlObject value, or std::nullopt if parsing failed
- * need to know if parsing succeeded.
+ */
+
+/**
+ * \fn template<typename T> YamlObject::get<T>(const T &defaultValue) const
+ * \brief Parse the YamlObject as a \a T value
+ * \param[in] defaultValue The default value when failing to parse
  *
- * \return Value as a bool type
+ * This function parses the value of the YamlObject as a \a T object, and
+ * returns the value. If parsing fails (usually because the YamlObject doesn't
+ * store a \a T value), the \a defaultValue is returned.
+ *
+ * \return The YamlObject value, or \a defaultValue if parsing failed
  */
 
 #ifndef __DOXYGEN__
 
 template<>
-bool YamlObject::get(const bool &defaultValue, bool *ok) const
+std::optional<bool> YamlObject::get() const
 {
-	setOk(ok, false);
-
 	if (type_ != Type::Value)
-		return defaultValue;
+		return {};
 
-	if (value_ == "true") {
+	if (value_ == "true")
-		setOk(ok, true);
 		return true;
-	} else if (value_ == "false") {
+	else if (value_ == "false")
-		setOk(ok, true);
 		return false;
-	}
 
-	return defaultValue;
+	return {};
 }
 
 template<>
-int16_t YamlObject::get(const int16_t &defaultValue, bool *ok) const
+std::optional<int16_t> YamlObject::get() const
 {
-	setOk(ok, false);
-
 	if (type_ != Type::Value)
-		return defaultValue;
+		return {};
 
 	if (value_ == "")
-		return defaultValue;
+		return {};
 
 	char *end;
 
@@ -157,22 +149,19 @@ int16_t YamlObject::get(const int16_t &defaultValue, bool *ok) const
 	if ('\0' != *end || errno == ERANGE ||
 	    value < std::numeric_limits<int16_t>::min() ||
 	    value > std::numeric_limits<int16_t>::max())
-		return defaultValue;
+		return {};
 
-	setOk(ok, true);
 	return value;
 }
 
 template<>
-uint16_t YamlObject::get(const uint16_t &defaultValue, bool *ok) const
+std::optional<uint16_t> YamlObject::get() const
 {
-	setOk(ok, false);
-
 	if (type_ != Type::Value)
-		return defaultValue;
+		return {};
 
 	if (value_ == "")
-		return defaultValue;
+		return {};
 
 	/*
 	 * libyaml parses all scalar values as strings. When a string has
@@ -183,7 +172,7 @@ uint16_t YamlObject::get(const uint16_t &defaultValue, bool *ok) const
 	 */
 	std::size_t found = value_.find_first_not_of(" \t");
 	if (found != std::string::npos && value_[found] == '-')
-		return defaultValue;
+		return {};
 
 	char *end;
 
@@ -193,22 +182,19 @@ uint16_t YamlObject::get(const uint16_t &defaultValue, bool *ok) const
 	if ('\0' != *end || errno == ERANGE ||
 	    value < std::numeric_limits<uint16_t>::min() ||
 	    value > std::numeric_limits<uint16_t>::max())
-		return defaultValue;
+		return {};
 
-	setOk(ok, true);
 	return value;
 }
 
 template<>
-int32_t YamlObject::get(const int32_t &defaultValue, bool *ok) const
+std::optional<int32_t> YamlObject::get() const
 {
-	setOk(ok, false);
-
 	if (type_ != Type::Value)
-		return defaultValue;
+		return {};
 
 	if (value_ == "")
-		return defaultValue;
+		return {};
 
 	char *end;
 
@@ -218,22 +204,19 @@ int32_t YamlObject::get(const int32_t &defaultValue, bool *ok) const
 	if ('\0' != *end || errno == ERANGE ||
 	    value < std::numeric_limits<int32_t>::min() ||
 	    value > std::numeric_limits<int32_t>::max())
-		return defaultValue;
+		return {};
 
-	setOk(ok, true);
 	return value;
 }
 
 template<>
-uint32_t YamlObject::get(const uint32_t &defaultValue, bool *ok) const
+std::optional<uint32_t> YamlObject::get() const
 {
-	setOk(ok, false);
-
 	if (type_ != Type::Value)
-		return defaultValue;
+		return {};
 
 	if (value_ == "")
-		return defaultValue;
+		return {};
 
 	/*
 	 * libyaml parses all scalar values as strings. When a string has
@@ -244,7 +227,7 @@ uint32_t YamlObject::get(const uint32_t &defaultValue, bool *ok) const
 	 */
 	std::size_t found = value_.find_first_not_of(" \t");
 	if (found != std::string::npos && value_[found] == '-')
-		return defaultValue;
+		return {};
 
 	char *end;
 
@@ -254,22 +237,19 @@ uint32_t YamlObject::get(const uint32_t &defaultValue, bool *ok) const
 	if ('\0' != *end || errno == ERANGE ||
 	    value < std::numeric_limits<uint32_t>::min() ||
 	    value > std::numeric_limits<uint32_t>::max())
-		return defaultValue;
+		return {};
 
-	setOk(ok, true);
 	return value;
 }
 
 template<>
-double YamlObject::get(const double &defaultValue, bool *ok) const
+std::optional<double> YamlObject::get() const
 {
-	setOk(ok, false);
-
 	if (type_ != Type::Value)
-		return defaultValue;
+		return {};
 
 	if (value_ == "")
-		return defaultValue;
+		return {};
 
 	char *end;
 
@@ -277,50 +257,38 @@ double YamlObject::get(const double &defaultValue, bool *ok) const
 	double value = std::strtod(value_.c_str(), &end);
 
 	if ('\0' != *end || errno == ERANGE)
-		return defaultValue;
+		return {};
 
-	setOk(ok, true);
 	return value;
 }
 
 template<>
-std::string YamlObject::get(const std::string &defaultValue, bool *ok) const
+std::optional<std::string> YamlObject::get() const
 {
-	setOk(ok, false);
-
 	if (type_ != Type::Value)
-		return defaultValue;
+		return {};
 
-	setOk(ok, true);
 	return value_;
 }
 
 template<>
-Size YamlObject::get(const Size &defaultValue, bool *ok) const
+std::optional<Size> YamlObject::get() const
 {
-	setOk(ok, false);
-
 	if (type_ != Type::List)
-		return defaultValue;
+		return {};
 
 	if (list_.size() != 2)
-		return defaultValue;
+		return {};
 
-	/*
+	auto width = list_[0]->get<uint32_t>();
-	 * Add a local variable to validate each dimension in case
+	if (!width)
-	 * that ok == nullptr.
+		return {};
-	 */
-	bool valid;
-	uint32_t width = list_[0]->get<uint32_t>(0, &valid);
-	if (!valid)
-		return defaultValue;
 
-	uint32_t height = list_[1]->get<uint32_t>(0, &valid);
+	auto height = list_[1]->get<uint32_t>();
-	if (!valid)
+	if (!height)
-		return defaultValue;
+		return {};
 
-	setOk(ok, true);
+	return Size(*width, *height);
-	return Size(width, height);
 }
 
 #endif /* __DOXYGEN__ */

test/yaml-parser.cpp

@@ -148,7 +148,6 @@ protected:
 		}
 
 		/* Test string object */
-		bool ok;
 		auto &strObj = (*root)["string"];
 
 		if (strObj.isDictionary()) {
@@ -161,27 +160,27 @@ protected:
 			return TestFail;
 		}
 
-		if (strObj.get<string>("", &ok) != "libcamera" || !ok) {
+		if (strObj.get<string>().value_or("") != "libcamera") {
 			cerr << "String object parse as wrong content" << std::endl;
 			return TestFail;
 		}
 
-		if (strObj.get<int32_t>(-1, &ok) != -1 || ok) {
+		if (strObj.get<int32_t>()) {
 			cerr << "String object parse as integer" << std::endl;
 			return TestFail;
 		}
 
-		if (strObj.get<uint32_t>(1, &ok) != 1 || ok) {
+		if (strObj.get<uint32_t>()) {
 			cerr << "String object parse as unsigned integer" << std::endl;
 			return TestFail;
 		}
 
-		if (strObj.get<double>(1.0, &ok) != 1.0 || ok) {
+		if (strObj.get<double>()) {
 			cerr << "String object parse as double" << std::endl;
 			return TestFail;
 		}
 
-		if (strObj.get<Size>(Size(0, 0), &ok) != Size(0, 0) || ok) {
+		if (strObj.get<Size>()) {
 			cerr << "String object parse as Size" << std::endl;
 			return TestFail;
 		}
@@ -199,27 +198,27 @@ protected:
 			return TestFail;
 		}
 
-		if (int32Obj.get<int32_t>(-100, &ok) != -100 || !ok) {
+		if (int32Obj.get<int32_t>().value_or(0) != -100) {
 			cerr << "Integer object parse as wrong value" << std::endl;
 			return TestFail;
 		}
 
-		if (int32Obj.get<string>("", &ok) != "-100" || !ok) {
+		if (int32Obj.get<string>().value_or("") != "-100") {
 			cerr << "Integer object fail to parse as string" << std::endl;
 			return TestFail;
 		}
 
-		if (int32Obj.get<double>(1.0, &ok) != -100.0 || !ok) {
+		if (int32Obj.get<double>().value_or(0.0) != -100.0) {
 			cerr << "Integer object fail to parse as double" << std::endl;
 			return TestFail;
 		}
 
-		if (int32Obj.get<uint32_t>(1, &ok) != 1 || ok) {
+		if (int32Obj.get<uint32_t>()) {
 			cerr << "Negative integer object parse as unsigned integer" << std::endl;
 			return TestFail;
 		}
 
-		if (int32Obj.get<Size>(Size(0, 0), &ok) != Size(0, 0) || ok) {
+		if (int32Obj.get<Size>()) {
 			cerr << "Integer object parse as Size" << std::endl;
 			return TestFail;
 		}
@@ -237,27 +236,27 @@ protected:
 			return TestFail;
 		}
 
-		if (uint32Obj.get<int32_t>(-1, &ok) != 100 || !ok) {
+		if (uint32Obj.get<int32_t>().value_or(0) != 100) {
 			cerr << "Unsigned integer object fail to parse as integer" << std::endl;
 			return TestFail;
 		}
 
-		if (uint32Obj.get<string>("", &ok) != "100" || !ok) {
+		if (uint32Obj.get<string>().value_or("") != "100") {
 			cerr << "Unsigned integer object fail to parse as string" << std::endl;
 			return TestFail;
 		}
 
-		if (uint32Obj.get<double>(1.0, &ok) != 100.0 || !ok) {
+		if (uint32Obj.get<double>().value_or(0.0) != 100.0) {
 			cerr << "Unsigned integer object fail to parse as double" << std::endl;
 			return TestFail;
 		}
 
-		if (uint32Obj.get<uint32_t>(100, &ok) != 100 || !ok) {
+		if (uint32Obj.get<uint32_t>().value_or(0) != 100) {
 			cerr << "Unsigned integer object parsed as wrong value" << std::endl;
 			return TestFail;
 		}
 
-		if (uint32Obj.get<Size>(Size(0, 0), &ok) != Size(0, 0) || ok) {
+		if (uint32Obj.get<Size>()) {
 			cerr << "Unsigned integer object parsed as Size" << std::endl;
 			return TestFail;
 		}
@@ -275,27 +274,27 @@ protected:
 			return TestFail;
 		}
 
-		if (doubleObj.get<string>("", &ok) != "3.14159" || !ok) {
+		if (doubleObj.get<string>().value_or("") != "3.14159") {
 			cerr << "Double object fail to parse as string" << std::endl;
 			return TestFail;
 		}
 
-		if (doubleObj.get<double>(1.0, &ok) != 3.14159 || !ok) {
+		if (doubleObj.get<double>().value_or(0.0) != 3.14159) {
 			cerr << "Double object parse as wrong value" << std::endl;
 			return TestFail;
 		}
 
-		if (doubleObj.get<int32_t>(-1, &ok) != -1 || ok) {
+		if (doubleObj.get<int32_t>()) {
 			cerr << "Double object parse as integer" << std::endl;
 			return TestFail;
 		}
 
-		if (doubleObj.get<uint32_t>(1, &ok) != 1 || ok) {
+		if (doubleObj.get<uint32_t>()) {
 			cerr << "Double object parse as unsigned integer" << std::endl;
 			return TestFail;
 		}
 
-		if (doubleObj.get<Size>(Size(0, 0), &ok) != Size(0, 0) || ok) {
+		if (doubleObj.get<Size>()) {
 			cerr << "Double object parse as Size" << std::endl;
 			return TestFail;
 		}
@@ -313,27 +312,27 @@ protected:
 			return TestFail;
 		}
 
-		if (sizeObj.get<string>("", &ok) != "" || ok) {
+		if (sizeObj.get<string>()) {
 			cerr << "Size object parse as string" << std::endl;
 			return TestFail;
 		}
 
-		if (sizeObj.get<double>(1.0, &ok) != 1.0 || ok) {
+		if (sizeObj.get<double>()) {
 			cerr << "Size object parse as double" << std::endl;
 			return TestFail;
 		}
 
-		if (sizeObj.get<int32_t>(-1, &ok) != -1 || ok) {
+		if (sizeObj.get<int32_t>()) {
 			cerr << "Size object parse as integer" << std::endl;
 			return TestFail;
 		}
 
-		if (sizeObj.get<uint32_t>(1, &ok) != 1 || ok) {
+		if (sizeObj.get<uint32_t>()) {
 			cerr << "Size object parse as unsigned integer" << std::endl;
 			return TestFail;
 		}
 
-		if (sizeObj.get<Size>(Size(0, 0), &ok) != Size(1920, 1080) || !ok) {
+		if (sizeObj.get<Size>().value_or(Size(0, 0)) != Size(1920, 1080)) {
 			cerr << "Size object parse as wrong value" << std::endl;
 			return TestFail;
 		}
@@ -351,27 +350,27 @@ protected:
 			return TestFail;
 		}
 
-		if (listObj.get<string>("", &ok) != "" || ok) {
+		if (listObj.get<string>()) {
 			cerr << "List object parse as string" << std::endl;
 			return TestFail;
 		}
 
-		if (listObj.get<double>(1.0, &ok) != 1.0 || ok) {
+		if (listObj.get<double>()) {
 			cerr << "List object parse as double" << std::endl;
 			return TestFail;
 		}
 
-		if (listObj.get<int32_t>(-1, &ok) != -1 || ok) {
+		if (listObj.get<int32_t>()) {
 			cerr << "List object parse as integer" << std::endl;
 			return TestFail;
 		}
 
-		if (listObj.get<uint32_t>(1, &ok) != 1 || ok) {
+		if (listObj.get<uint32_t>()) {
 			cerr << "List object parse as unsigne integer" << std::endl;
 			return TestFail;
 		}
 
-		if (listObj.get<Size>(Size(0, 0), &ok) != Size(0, 0) || ok) {
+		if (listObj.get<Size>()) {
 			cerr << "String list object parse as Size" << std::endl;
 			return TestFail;
 		}
@@ -424,27 +423,27 @@ protected:
 			return TestFail;
 		}
 
-		if (dictObj.get<string>("", &ok) != "" || ok) {
+		if (dictObj.get<string>()) {
 			cerr << "Dictionary object parse as string" << std::endl;
 			return TestFail;
 		}
 
-		if (dictObj.get<double>(1.0, &ok) != 1.0 || ok) {
+		if (dictObj.get<double>()) {
 			cerr << "Dictionary object parse as double" << std::endl;
 			return TestFail;
 		}
 
-		if (dictObj.get<int32_t>(-1, &ok) != -1 || ok) {
+		if (dictObj.get<int32_t>()) {
 			cerr << "Dictionary object parse as integer" << std::endl;
 			return TestFail;
 		}
 
-		if (dictObj.get<uint32_t>(1, &ok) != 1 || ok) {
+		if (dictObj.get<uint32_t>()) {
 			cerr << "Dictionary object parse as unsigned integer" << std::endl;
 			return TestFail;
 		}
 
-		if (dictObj.get<Size>(Size(0, 0), &ok) != Size(0, 0) || ok) {
+		if (dictObj.get<Size>()) {
 			cerr << "Dictionary object parse as Size" << std::endl;
 			return TestFail;
 		}